1. Field of Use
This invention relates to printed wiring boards and more particularly to systems and methods for fabricating such boards.
2. Prior Art
As is well known, printed wiring board designs are developed through the utilization of computer aided design (CAD) systems. These systems have interactive graphic and digitizing equipment used by a designer during the physical design and layout phases of a multilayer printed circuit board development.
Such CAD systems are used to provide a digitized output on a magnetic media. The output is in turn applied as an input to photoplotting equipment which generates the PWB artwork. The artwork is then used to fabricate the prototype or production version of the printed wiring board by employing well known photography and manufacturing steps.
It has been found that dissimilarities in the manufacturing steps or processes for fabricating double sided and multilayer printed wiring boards have given rise to problems in the amount of plating on both sides of a printed wiring board panel as it proceeds through the plating cycle. For example, in a panel plate operation/process, the panels are first drilled and then metal, such as copper, is deposited on both sides of the panel to the desired finish thickness. The artwork image is then photographically applied to or stenciled on the panel. The unwanted metal is etched away leaving the desired pattern.
By contrast, in a selective plating operation or pattern plate, a similar photographic stenciling operation is used. However, the pattern covers only those areas where metal is not desired. Since in selective plating all the plating is not done before image application, the circuit pattern densities are of less concern and can be relatively uncontrolled.
When you take circuit board design artworks developed for a panel plate operation to facilitate boards using a pattern plate process, significant plating unbalances result. One technique used to reduce such imbalances has been to take circuit pattern densities into account during the design phase. In addition to restricting the designer, it requires expenditure of extra effort to ensure circuit patterns are uniformly distributed adding to design complexity as well as manually lengthening the design phase.
Another technique has been to employ a method of unsystematic taping wherein tape is added to the sides of the boards to assist in the plating process. In addition to being very time consuming, in many cases the tape had to be removed to prevent the boards from becoming non-functional.
The above problems are further compounded by the number of boards which are being fabricated, as well as the number of layers. Each board type in many cases requires special handling by individual inspection and testing. The result is marked decreases in production throughput.
Accordingly, it is a primary object of the present invention to provide a method for facilitating the fabrication of printed wiring boards.
It is a further object of the invention to provide a method which increases production throughput and reduces both the design and fabrication cycle time.
It is still a further object of the invention to provide a system and method which permits high volume production for all types of boards at significant cost savings.